This invention relates to printed circuitry techniques and, more particularly, this invention relates to the method for making precision thick film capacitors having predetermined values.
A common method for fabricating a precision thick film ceramic capacitor requires: Printing in registry an upper and lower plate on a ceramic substrate; measuring the value of the capacitance with respect to said plates; abrasively cutting away or using a laser burning away the portion of one plate of the capacitor and thereby decreasing the capacitance value to the value desired.
The prior art method of trimming down the capacitance value of a thick film capacitor to a precision value by cutting away a portion of one plate of the capacitor has certain disadvantages. First, the capacitance value may only be adjusted downward. As a consequence, should the capacitance value be trimmed beyond the point desired, readjustment is impossible. Secondly, trimming by this method leaves an unprotected edge of the capacitor plate which decreases its reliability due to susceptibility to attack by moisture, dirt, or chemicals.
Accordingly, it is a primary object of this invention to provide a precision thick film capacitor having a predetermined value.
Another object of the present invention is the elimination of the requirement of a cutting away of a portion of a plate of a ceramic thick film capacitor in order to achieve a precise value thereof.
Still another object is a method of producing thick film parallel plate capacitors in incremental values with the same plate pattern and area.
These and other objects are accomplished in accordance with the teaching of the present invention.